The present invention relates to an improved non-woven fibrous product and more specifically to a non-woven product of mineral and man-made fibers which exhibits improved strength and toughness. The man-made, i.e., synthetic, fibers are of two kinds: standard homogeneous fibers and fibers having a high melting point core and low melting point sheath. The blanket may be formed into sheets, panels and complexly curved and configured products.
Non-woven fibrous products including sheets and panels as well as other thin-wall products such as insulation and complexly curved and shaped structures formed from such planar products are known in the art
In U.S. Pat. No. 2,483,405, two distinct types of fibers therein designated non-adhesive and potentially adhesive fibers are utilized to form a non-woven product The potentially adhesive fibers typically consist of a thermoplastic material which are mixed with non-adhesive fibers to form a blanket, cord or other product such as a hat. The final product is formed by activating the potentially adhesive fibers through the application of heat, pressure or chemical solvents Such activation binds the fibers together and forms a final product having substantially increased strength over the unactivated product.
U.S. Pat. No. 2,689,199 relates to non-woven porous, flexible fabrics prepared from masses of curled, entangled filaments. The filaments may be various materials such as thermoplastic polymers and refractory fibers of glass, asbestos or steel. A fabric blanket consisting of curly, relatively short filaments is compressed and heat is applied to at least one side to coalesce the fibers into an imperforate film. Thus, a final product having an imperforate film on one or both faces may be provided or this product may be utilized to form multiple laminates. For example, an adhesive may be applied to the film surface of two layers of the product and a third layer of refractory fibers disposed between the film surfaces to form a laminate.
In U.S. Pat. No. 2,695,855, a felted fibrous structure which incorporates a rubber-like elastic material and a thermoplastic or thermosetting resin material is disclosed. The mat or felt structure includes carrier fibers of long knit staple cotton, rayon, nylon or glass fibers, filler fibers of cotton linter or nappers, natural or synthetic rubber and an appropriate resin. The resulting structure of fibers intimately combined with the elastic material and resinous binder is used as a thermal or acoustical insulating material and for similar purposes.
U.S. Pat. No. 4,568,581 teaches a method of manufacturing and an article comprising a non-woven blend of relatively high melting point fibers and relatively low melting point fibers. At one surface of the article the low melting point fibers have a fibrous form and at the opposite surface they exhibit a non-fibrous, fused form.
U.S. Pat. No. 4,612,238 discloses and claims a composite laminated sheet consisting of a first layer of blended and extruded thermoplastic polymers, a particulate filler and short glass fibers, a similar, second layer of a synthetic thermoplastic polymer, particulate filler and short glass fibers and a reinforcing layer of a synthetic thermoplastic polymer, a long glass fiber mat and particulate filler. The first and second layers include an embossed surface having a plurality of projections which grip and retain the reinforcing layer to form a laminate.
One of the inherent difficulties of the non-woven plural component mat products discussed above relates to the character and strength of the fiber-to-fiber bonds. When a thermoplastic resin is utilized, a significant portion of the resin particles reside in locations within the fiber matrix where their melting and adhering provide little or no benefit. This occurs wherever a resin particle, rather than bridging and securing two adjacent fibers merely melts on or around a single fiber. Since there is no way to ensure the emplacement of resin particles only at fiber junctions, an excess of resin must be utilized in the blanket in order to assure that sufficient bonds do develop to produce the requisite strength in the final product. This increases the cost of the final product. Conversely, not all fiber junctions receive sufficient resin to create a fiber-to-fiber bond. Accordingly, unless an excessive amount of thermosetting resin is added to the fiber blanket, it will not exhibit the strength and ruggedness theoretically possible because many junction bonds are absent.
The use of low and high melting point fibers as suggested in U.S. Pat. Nos. 2,983,405 or 4,568,581 does not entirely solve this difficulty. If the low melting point fiber is sufficiently melted to provide adhesion to another, higher melting point fiber, it may melt and completely lose its structure. Since low melting point thermoplastics are typically relatively flexible and resilient and are utilized in such products for these characteristics, the melting and agglomeration of the fiber into adherent junctions of the other fibers will result in a loss of resilience to the product.
It is apparent from the foregoing review of non-woven mats, blankets and felted structures that variations and improvements in such prior art products are not only possible but desirable.